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Electrical trouble with my Delta grinder.....need advice.

Odie

Odie

Panning for Montana gold, with Betsy, the mule!
TOTW Team
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Dec 22, 2006
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For the first time this evening, I had some trouble starting my grinder. When flipping the switch, it buzzed and didn't rotate the grind wheels. A couple times the wheels went backwards for about an inch at the wheel surface and stopped. If I gave the wheels a spin, and then flipped the switch, it would come up to speed, but the acceleration was slow.

Is this a bad thing to give the wheels a spin, and then flip the switch?

The information on the motor plate is as follows:

Delta model 23-725
1800 rpm
3/4 hp
1ph 10a
serial # 2007 29-YL-1899

It's on a 110v circuit.

Will the motor need a rebuild, or is this a simple part replacement? (capacitor maybe?)

I haven't removed the grinder from it's stand, so haven't looked into the internal components of the motor base yet. All this happened about 1/2hr ago, as I type, so thought I'd get some advice before I start to break the grinder and set-up down.

Any thoughts are appreciated.

-----odie-----

IMG_4151.JPG
 
Was there a foul odor to go along with the behavior? I had a clothes washer that lost it's motor capactor twice, each time barfing its guts inside the machine and making quite a stink. After the second time I replaced it (not a terrible or expensive task, just very inconvenient when the machine was now full of soapy water and clothes) I started shopping for a new washer. That capacitor was about half the size of a beer can.
 
I had a different problem with a DELTA variable speed grinder, but my interim fix might help you in the interim. I mounted a heavy CBN wheel on the grinder and found that in very cold weather it didn’t have the strength to start up before blowing a fuse in the base. I replaced the fuse several times before I got to a permanent fix, but to avoid the issue, I chucked a socket that fit the nut holding the wheel on the grinder in a drill and spun it up to speed with the drill, slipping it off the nut and turning the grinder on while it was spinning. The more permanent fix, which has worked for over two years now, was to up the amperage of the slow-blow fuse in the base of the grinder. I only did this after consulting with an electronics expert at an AAW symposium - (thank you very much!), who assured me I would not be doing any damage to the grinder. So far, so good!
 
odie said:
I'm still on my 2nd grinder, and it sees constant use for the last 20+ years. So far, so good......no problems at all. I consider it top notch, an old-school Delta that is no longer available. It's an industrial grade grinder, IMHO.

If my Delta ever fails me, I will get the 8" Baldor. I may not have owned a Baldor personally, but for the last 20 years of my working life (I'm now retired), I worked in a shop that had about 50 Baldor motors used for polishing, and shaping medical tools. (I worked in the machine shop of that company.) I can safely say the Baldor motors are built to industrial standards and last a long long time. This is not to say that they don't eventually wear out......they do, but it takes a lot of use, and abuse.
Click to expand...

Odie, Your Delta did not take kindly to you talking about replacement.
 
I agree with the start capacitor diagnosis. It's probably located in the base of your grinder. It'll be the one with wires going into it. The important part is to get the mf number and voltage off the side of the capacitor. I've had good luck finding the correct replacement capacitor off Ebay. Usually about $10-$15 after you figure in shipping.
 
Grinders do not need a lot of starting torque so it probably does not have a starting capacitor, but it likely has a centrifugal switch that opens the circuit to the start windings when it gets up to speed. The buzz and the spinning to get it started would likely indicate a problem with the centrifugal switch or the start windings.
 
Don Wattenhofer said:
Grinders do not need a lot of starting torque so it probably does not have a starting capacitor, but it likely has a centrifugal switch that opens the circuit to the start windings when it gets up to speed. The buzz and the spinning to get it started would likely indicate a problem with the centrifugal switch or the start windings.
Click to expand...
It does have a capacitor.
 
Mine had a start capacitor in the base under the bottom plate. I had to replace it after I put on a heavy CBN wheel and let the magic smoke out. I since upgraded to a 1 hp grinder for the CBN wheels.
 
Odie, it appears that your capacitor is not available from Delta or ereplacements.com. If you look at that capacitor on your grinder, it should have a uF (or mF) value and a voltage value. You can order a replacement with the same values from Grainger, Zoro, www.supplyhouse.com or by doing an online search. If you have problems, please post a picture of the markings on the capacitor.

Larry
 
Odie, before you rush out to buy a start capacitor, try this simple trick: Blow compressed air through the body of the motor and see if it solves your problem. If it doesn't, spin the motor up by hand to get it started and repeat the compressed air thing. Sometimes, a bit of grit or a chip lodges beween the contacts of the centrifugal start switch that switches the capacitor in and out. I have had this happen twice; once on a craftsman radial arm saw and once on a Delta grinder.
 
"a bit of grit or a chip lodges between the contacts of the centrifugal start switch"
That does happen and is a simple solution.
Off topic a bit but this is where the statement of "having a bug in it" started. Old (read that as ancient) computers had contact switches. Yes, a bug got between the contacts and wouldn't allow them to shut and make connection.
 
Since it is a totally closed motor, there is little chance of dirt getting in there, but the contacts of the centrifugal switch can be burned preventing the starting circuit from energizing. if the capacitor looks good and not bulging it could be the contacts, though I still would exchange the capacitor for a new one first, rather than pulling the motor apart, they rarely get better from that. just IMO 1thumb.gif
 

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Lou Jacobs said:
I had a different problem with a DELTA variable speed grinder, but my interim fix might help you in the interim. I mounted a heavy CBN wheel on the grinder and found that in very cold weather it didn’t have the strength to start up before blowing a fuse in the base. I replaced the fuse several times before I got to a permanent fix, but to avoid the issue, I chucked a socket that fit the nut holding the wheel on the grinder in a drill and spun it up to speed with the drill, slipping it off the nut and turning the grinder on while it was spinning. The more permanent fix, which has worked for over two years now, was to up the amperage of the slow-blow fuse in the base of the grinder. I only did this after consulting with an electronics expert at an AAW symposium - (thank you very much!), who assured me I would not be doing any damage to the grinder. So far, so good!
Click to expand...
I had the same issue with my variable speed Delta when I switched to CBN wheels. Unfortunately, after blowing several fuses, I scrapped it and bought a couple of 3,600 rpm grinders. This thread came about a year too late!!
 
Leo Van Der Loo said:
Since it is a totally closed motor, there is little chance of dirt getting in there, but the contacts of the centrifugal switch can be burned preventing the starting circuit from energizing. if the capacitor looks good and not bulging it could be the contacts, though I still would exchange the capacitor for a new one first, rather than pulling the motor apart, they rarely get better from that. just IMO View attachment 37026
Click to expand...

Leo......(Thanks for the diagram. :D)

And thanks to everyone else for all the helpful responses.....I appreciate that! :D

I think the centrifugal switch is working. I noticed that "click" sound at a slower rpm when I turned off the motor. This, after starting it by giving it a spin manually.

Yes, it is a totally enclosed motor.

We have a Pratt electrical wholesale supply here, and I ordered another start capacitor, but another brand. I'm not knowledgeable here, but the clerk there seemed to know what he was doing. The new start capacitor was not expensive, but won't be here until Monday, at the earliest.

As requested, here is a photo of the old capacitor. It does not appear to be bulged.

-----odie-----

IMG_6436.JPG
IMG_6437.JPG IMG_6438.JPG
 
Kevin Weir said:
I had the same issue with my variable speed Delta when I switched to CBN wheels. Unfortunately, after blowing several fuses, I scrapped it and bought a couple of 3,600 rpm grinders. This thread came about a year too late!!
Click to expand...
I don't believe a variable speed single phase motor would have a starting capacitor or starting windings and centrifugal switch so your problem is something altogether different.
 
Odie, I was away from my computer all day so I didn't see your thread until now. I can feel your pain because I have the same model grinder. You have done an excellent job of doing all the right things to troubleshoot the problem.

Richard Hodsdon is right, the symptoms you described are exactly what happens when the start capacitor goes bad and sometimes a bad capacitor looks just like a good one. There is a small possibility that the centrifugal switch has a problem, but if that is the case you can usually repair it yourself. Let's hope that the capacitor fixes the problem so that you won't have to disassemble the motor. I can help guide you through the process of repairing the switch if necessary. The worst case scenario would be the start winding has failed, but we don't even want to think about that because it would leave you with the choice of getting a new grinder (and, there aren't any in the same league as the Delta unless you go with an industrial grinder $$$$) or have the start winding rewound (and, even if you could find a shop that rewinds motors, I was told by a guy who has such a business locally that they only rewind very expensive large industrial motors). Things are different than they were fifty years ago.
 
I recall reading in another thread that once disconected these capacitors can still retain their charge for a very very long time. What is the proper procedure to discharge them?
 
Mark, yes, when I replaced the magnetron in my microwave, loads of cautions on YouTube about discharging the capacitor by shorting it out before taking parts out to avoid death! (Disclaimer: I’m not an electrician or EE, so take this with a grain of salt).
 
I'm sure others have had this same experience - my high school auto shop teacher used to leave charged condensers (capacitor) laying around for us to pick up and enjoy!

This, of course, was back in the day of good old points/condenser ignitions on cars!
 
Kevin Weir said:
I had the same issue with my variable speed Delta when I switched to CBN wheels. Unfortunately, after blowing several fuses, I scrapped it and bought a couple of 3,600 rpm grinders. This thread came about a year too late!!
Click to expand...

To bad Kevin, a single phase motor is unable to start without an opposing field to get it going, (that is why you need a starter winding, and a disconnect so that winding does not burn out) we used to sell single phase farmer duty motors on pumps that did not have a starter winding, these had to be started by winding a rope around the shaft and giving it a pull, then switching it on, (this is more than 60 years ago) they could be run in either direction, so that was handy for some other applications, where the same motors could be used and run in the opposing direction, plus the motors did cost a lot less ;-))

Single phase motor.jpg
 
Last edited:
Question regarding the centrifugal switch......

Just wondering.....

I can hear the "click" of the centrifugal weights on shut off, so I'm assuming that mechanism is working. Now, if the contact points were burned, and stuck in the closed position, wouldn't the extra power on start up be permanently activated? Or, is the extra power applied when the contact points are open? At this point, it appears as though the extra power boost is not activated at all.

I expect the new starting capacitor to be here on Monday, but if I find that isn't the problem, then the only other option (?) is the centrifugal switch?

-----odie-----
 
Mark Jundanian said:
I recall reading in another thread that once disconected these capacitors can still retain their charge for a very very long time. What is the proper procedure to discharge them?
Click to expand...

Yes, it can take many minutes for the voltage to fall to safe levels. For a 120 V RMS input, the stored voltage with respect a given terminal can range from about -170 V to + 170 V, depending on the phase of the AC input at the instant of disconnect.
 
odie said:
Question regarding the centrifugal switch......

Just wondering.....

I can hear the "click" of the centrifugal weights on shut off, so I'm assuming that mechanism is working. Now, if the contact points were burned, and stuck in the closed position, wouldn't the extra power on start up be permanently activated? Or, is the extra power applied when the contact points are open? At this point, it appears as though the extra power boost is not activated at all.

I expect the new starting capacitor to be here on Monday, but if I find that isn't the problem, then the only other option (?) is the centrifugal switch?

-----odie-----
Click to expand...
Odie if the contacts are welded together, the magic smoke would come out pretty quick, the startup winding is not able to be energized for a long time, it will burn out, that is what normally would occur.

When the motor is at standstill the contacts are closed, and power will go to the main and startup winding, as soon as the motor spins up the weights of the centrifugal switch move outwards and then the contacts are apart/open.

So yes the power is not to the starting winding or it should be starting up, we hope that that is the case and that the winding is not burned out :D
 
I'm sure the new condenser will solve your problem. I've replaced mine once in the 20 years I've had the grinder and it had the exact issue you describe. BTW, the heavier steel (vs. aluminum) 8" CBN wheels will cause the grinder to also struggle to get started. When I put the CBNs on it a couple years ago, I thought the second condenser had given out but a replacement didn't solve the issue. I now give it a little boost by getting the wheels rotating and then turn it on -- works fine.

For the electrical gurus in the group, will a different mf rating on the condenser address the problem with starting heavier loads? Any other solution? (I really like the grinder otherwise and always have my eye out for a used Baldor, but so far no luck given the $.)
 
Leo Van Der Loo said:
Odie if the contacts are welded together, the magic smoke would come out pretty quick, the startup winding is not able to be energized for a long time, it will burn out, that is what normally would occur.

When the motor is at standstill the contacts are closed, and power will go to the main and startup winding, as soon as the motor spins up the weights of the centrifugal switch move outwards and then the contacts are apart/open.

So yes the power is not to the starting winding or it should be starting up, we hope that that is the case and that the winding is not burned out :D
Click to expand...


OK.....I never did see, or notice any smoke, so the new condenser should solve my problems. Thank you for responding in such a way that dummies like me can make sense of what's going on!.......:D

-----odie-----
 
The one on the left is the new capacitor, and the one on the right is the old one......are these two similar enough to call it good?

I could hook up the new capacitor and try it, but I'm not sure it won't cause any damage to my grinder motor......

-----odie-----

IMG_6462.JPG
 
They do make meters that can test the capacity and function of a capacitor, you can also use a simple multimeter to test if the capacitor is functional or shorted out.
Plenty of YouTube videos show the basic procedure, they will bite you if you touch the leads on a charged capacitor. .
 
I replaced the start capacitor on my air compressor with one that had a range of capacitance on it. The old one was smack in the middle of the range and said something like +/- 5 mf. Fired it up and out came the magic smoke. The lid had blown off. When I contacted the seller of the capacitor, he said, "you didn't buy the right capacitor". the new capacitor's lower end of the range was below the old one's single point. I thought he was blowing me off and would not buy from that particular seller/brand again. But maybe he's right. Most of the capacitors I saw listed had a range specified rather than a single number.

Odie--in my very limited experience, the visible part of magic smoke is not as obvious as the smell. Since your capacitor was tucked under the base of the grinder, it would be possible to miss seeing it blow.
 
I suspect that the range is the range of values within which the capacitance must lie to be accepted for that part number. If the motor is starting under low load conditions, such as in a grinder, the exact capacitance value is not at all critical.
 
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